For the terrorists behind this attack, big questions about who they are and conflicting reports about whether americans were involved. The kenyan foreign minister making claims that several u.S. Citizens were part of this massive attack. Brian ross has been digging into this part of the story. Reporter: The kenyan foreign minister was in new york monday. And told pbs that two or three young american men were among the attackers. Describing them as 18 years old or 19 years old. And the fbi cannot confirm her claims. And there's no reliable information whether americans were involved. And the same foreign minister mentioned the possibility of a british woman being involved. Reporter: She did. She said there's a woman involved in this. And the british foreign office has told us they can't confirm that, either. Kenyan officials on the ground told us there were no women, but men dressed as women. These reports are contradictory. And perhaps the kenyan president will sort it all out at a news conference today. An extremely aggressive group, as we saw there. And there's concern about here. What is known as a fact, that many americans, 50 americans, have been recruited to go there. Many have been killed. Some of them brought back here and charged. But there's a number of americans in that group, somewhere in africa. And there's great concern that what they've learned in africa, they could bring home here. Brian, thanks so much. Now, to president obama's

This transcript has been automatically generated and may not be 100% accurate.

Kenyan Forces Take Control of Mall, Search for Terrorists

Military is sweeping the Westgate mall searching for the attackers and detonating explosives.

Obama Offers Kenya President Support

ABC News' Jon Karl discusses the White House reaction to the attack and looming government shutdown.

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